Does it work? Mercedes Eco Assist: the car that helps you drive better

Published: 21 November 2017

► Mercedes Eco Assist
► The S-class that helps you drive better
► Encouraging or irritating?

Amid all the excitement over Mercedes’ latest evolution of its autonomous driving systems in the revised S-Class, it’s easy to overlook the other big innovation: you.

More precisely, the S is set up to offer encouragement, information and incentives to help you drive more smoothly and more economically. Crucially, it can be ignored and over-ridden, leaving you to decide whether your priority is economy at any given moment.

The latest, upgraded version of Eco Assist is available on the S450 (not a UK model) and S500 – the only cars using new beltless inline-six petrol engine with 48-volt electrics and an integrated starter-generator (ISG) instead of an alternator. 

Eco Assist works by combining several features. Connectivity and sensors: The car knows where you are, where you’re going, and what’s happening in between. So it won’t encourage you to accelerate towards slowing traffic or a hairpin, for instance. 

Coasting: The engine can turn itself off and on again at motorway speeds, and engage neutral while it’s coasting, if it calculates that a period of being propelled purely by momentum (and the subsequent restart) will be more economical than keeping the engine on throughout. 

Recuperation: The ISG system has a soft-hybrid element, so it can store surplus braking energy in its second battery. It’s constantly calculating whether cruising or braking (and storing the resultant energy) is better in the current circumstances. 

Adaptive cruise control: The latest S-Class has a refined version of ACC, factoring in everything from the weather and the road surface to the route and the charge level of the battery as it calculates the best way to keep you at a safe distance from other traffic while using as little fuel as possible.

Mercedes Eco Assist interior

Eco Assist is there all the time, making background calculations about when best to intervene and in what way. But there are several instances where it can make a big difference (see above).

And Merc’s latest stop-start system – clever enough to stop the engine while the car is still moving – uses all the information available through GPS, radar etc to avoid infuriating sub-two-second switch offs. As well as being annoying, they’re less fuel efficient than keeping the engine on.

When Eco Assist helps most


You’re prompted to lift your foot off the gas, and the car will brake itself.


The mapping knows you’re near the brow of a hill and will prompt you to lift off.

Moving queues

If the radar spots you’re cruising into a queue, it slows but aims to keep rolling.

Did it work?

Yes. It’s amazing how seamless the transition is between engine-off coasting, recuperation and conventional propulsion.

If you ignored the info on the dash, you could easily not know what was going on under the bonnet. The lights and icons are subtle enough to fall into the category of useful information rather than nannying interference.

Mercedes has made a point of programming the system to avoid an excessive number of prompts. It’s very grown-up. 

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By Colin Overland

CAR's managing editor: wordsmith, critic, purveyor of fine captions